Why No Flu Pandemic? Define Pandemic : Shots - Health NewsWHO will not declare that swine flu, or H1N1, has reached pandemic proportions. But it's leaving open the question for now of whether it will change its own definition of exactly what would trigger a pandemic.

Why No Flu Pandemic? Define Pandemic

Margaret Chan, the World Health Organization's director-general, has decided not to declare that the world has entered the first flu pandemic of this century.

But she's leaving open the question -- for now -- of changing the definition of a pandemic.

Chan declared on April 29 that a flu pandemic is "imminent." But she's been under increasing pressure from WHO's member-states to hold off declaring that a pandemic has arrived, based on the WHO's own definition.

Chan now says there's no doubt swine flu will continue to spread -- within the 42 countries already affected and beyond.

By saying that, Chan essentially acknowledges what many have been saying: This genie is out of the bottle.

It's getting harder by the day for WHO to say that "sustained widespread community transmission" is not underway in Japan, where the number of confirmed cases has jumped from four to nearly 300 in less than a week. Japanese officials themselves are reportedly on the brink of declaring widespread flu in several southwestern prefectures.

"This is a very contagious virus," Chan told the closing session of the annual World Health Assembly. " We expect it to continue to spread to new countries and continue to spread within countries already infected. Here, we have little doubt."

But there's a lot of doubt, she says, about what the new H1N1 virus is going to do, so the best-laid plans need to be flexible, Chan says.

But she left conspicuously unsaid whether WHO now will change its rules -- redefining just what a flu pandemic is to reflect severity of disease and not just geographic spread.

Maybe some hint of that will emerge at a briefing later this morning by Dr. Keiji Fukuda, Chan's chief deputy for influenza.